I. Field of the Invention
Embodiments of this invention are directed generally to the field of the use of biomarkers and bacteria. In certain aspects the invention is directed to methods for detecting bacterial contamination in samples by detecting a protein in the N-methyl-2 superfamily.
II. Description of the Related Art
The detection of bacteria is important in medical and veterinary microbiology, food safety, drinking water treatment, and many other areas. In particular, diagnosis of bacterial infections by detecting the causative bacteria is crucial to treatment of these common diseases.
Methods to diagnose the presence of bacteria include laboratory culture of samples to allow growth of the infectious agent on nutrient medium; detection of bacterial DNA sequences by polymerase chain reaction (PCR) or other methods; and direct detection of bacteria by chemical dyes and stains followed by microscopic examination (Ryan 2004). Major drawbacks of these methods include the laborious nature of the techniques and the time required to obtain a result—often more than a day in a typical laboratory. Most techniques also require a sample to be collected and transported to a laboratory capable of performing the test, adding additional time to obtain a result. In addition, some techniques require a pre-selection of which strains or species can be detected by a particular assay—for example, PCR detection necessitates the use of specific DNA sequences from bacterial species suspected of being present.
Immunoassays using specific antibodies binding to bacterial determinants are also known. These immunoassays are generally used following the culture of a particular sample to expand the number of bacteria present. In most such immunoassays, the antibodies are specific to particular strains of bacteria, serving to identify whether a population of bacteria contains a particular strain—often related to the serotype antigenic classification. Specific immunoassays exist to identify E. coli O157:H7 and other pathogenic strains (Kim 1992; Bennett; 1996).
For example, lateral flow immunochromatographic tests exist that detect the presence of E. coli O157:H7 in food and agricultural products following enrichment culture of any bacteria present (Neogen Corporation, Lansing, Mich.) (Kim 1992). This assay detects only a narrow range of enterotoxic E. coli strains. The assay uses antibodies specific for the 0157 and H7 determinants, neither of which is a member of the N-methyl-2 superfamily. Another example of immunoassays detecting bacteria is the Premier™ ELISA detecting Clostridium difficile in stool specimens (Meridian Bioscience, Cincinnati, Ohio). This assay uses the enzyme glutamate dehydrogenase (GDH) as the biomarker for the presence of Clostridium difficile in stool samples, and comprises antibodies capable of binding to GDH. GDH is not a member of the N-methyl-2 superfamily. Another example is the Watersafe® Bacteria Test (SLRC, Monrovia, Calif.), a lateral flow immunochromatographic test strip detecting high levels of some strains of E. coli and Pseudomonas aeruginosa in swimming pools. This test uses monoclonal antibodies that are not specific for proteins of the N-methyl-2 superfamily.
However, there remains a need for methods to detect a broad range bacteria in a sample.